This library streamlines returning HttpResults from endpoints that leverage CSharpFunctionalExtensions by offering convenient extension methods to map you result to an HttpResult.
With these, you can maintain a fluent, railway-oriented style by simply invoking the appropriate method at the end of your result chain.
It also supports custom error types and ensures a clear separation between your domain logic and API by using specific mappers to translate domain details into API responses.
[!TIP]
This library references a fairly old version of CSharpFunctionalExtensions for compatibility reasons.
It's recommended to also install the latest version of CSharpFunctionalExtensions in your project to get the latest features and fixes.
Usage
This library provides you extension methods to map the following Result types to HttpResults:
Discards value of Result<T> and returns NoContent or ProblemHttpResult
.ToNoContentHttpResult<T,E>()
Discards value of Result<T> and returns NoContent or custom error
.ToNoContentHttpResult<E>()
Returns NoContent or custom error
.ToCreatedHttpResult<T>()
Returns Created<T> or ProblemHttpResult
.ToCreatedHttpResult<T,E>()
Returns Created<T> or custom error
.ToCreatedAtRouteHttpResult<T>()
Returns CreatedAtRoute<T> or ProblemHttpResult
.ToCreatedAtRouteHttpResult<T,E>()
Returns CreatedAtRoute<T> or custom error
.ToAcceptedHttpResult<T>()
Returns Accepted<T> or ProblemHttpResult
.ToAcceptedHttpResult<T,E>()
Returns Accepted<T> or custom error
.ToAcceptedAtRouteHttpResult<T>()
Returns AcceptedAtRoute<T> or ProblemHttpResult
.ToAcceptedAtRouteHttpResult<T,E>()
Returns AcceptedAtRoute<T> or custom error
.ToFileHttpResult<byte[]>()
Returns FileContentHttpResult or ProblemHttpResult
.ToFileHttpResult<byte[],E>()
Returns FileContentHttpResult or custom error
.ToFileStreamHttpResult<Stream>()
Returns FileStreamHttpResult or ProblemHttpResult
.ToFileStreamHttpResult<Stream,E>()
Returns FileStreamHttpResult or custom error
.ToContentHttpResult<string>()
Returns ContentHttpResult or ProblemHttpResult
.ToContentHttpResult<string,E>()
Returns ContentHttpResult or custom error
All methods are available in sync and async variants.
Default mapping
By default, Result and Result<T> failures get mapped to a ProblemHttpResult based on RFC9457.
The status property contains the status code of the HTTP response. Note: For almost every method you can override the default status codes for Success/Failure case.
The type property contains a URI to the corresponding RFC9110 entry based on the status code.
The title property contains a generic short messages based on the status code.
The detail property contains the error string of the Result.
You don't have to provide the whole dictionary but can also override or add only mappings for specific status codes like this:
ProblemDetailsMappingProvider.AddOrUpdateMapping(420, "Enhance Your Calm", "https://http-status-code.de/420/");
It's recommended to override the mappings during startup e.g. in Program.cs.
Override mapping for single use case
If you need to override the mapping for a specific use case in a single location, you can provide an Action<ProblemDetails> to fully customize the ProblemDetails. This is particularly useful when you want to add extensions or tailor the ProblemDetails specifically for that use case.
When using Result<T,E> or UnitResult<E>, this library uses a Source Generator to generate extension methods for your own custom error types.
Create a custom error type
public record UserNotFoundError(string UserId);
Create a mapper that implements IResultErrorMapper which maps this custom error type to an HttpResult / IResult that you want to return in your Web-API:
public class UserNotFoundErrorMapper : IResultErrorMapper<UserNotFoundError, ProblemHttpResult>
{
public ProblemHttpResult Map(UserNotFoundError error)
{
var problemDetails = new ProblemDetails
{
Status = 404,
Title = "User not found",
Type = "https://tools.ietf.org/html/rfc9110#section-15.5.5",
Detail = $"The user with ID {error.UserId} couldn't be found.
};
return TypedResults.Problem(problemDetails);
};
}
Use the auto generated extension method:
app.MapGet("/users/{id}", (string id) => {
return userRepository.Find(id) //Result<User,UserNotFoundError>
.ToOkHttpResult(); //Results<Ok<User>,ProblemHttpResult>
});
[!IMPORTANT]
Make sure that every custom error type has exactly one corresponding IResultMapper implementation.
You can use the ProblemDetailsMappingProvider.FindMapping() method to find a suitable title and type for a status code based on RFC9110.
[!TIP]
If extension methods for custom errors are missing, rebuild the project to trigger Source Generation.
Analyzers
This library includes analyzers to help you use it correctly.
For example, they can notify you if you have multiple mappers for the same custom error type.
You can find a complete list of all analyzers here.
You're welcome to contribute. Please keep these few rules in mind:
add documentation in the form of summary comments
add tests for your additions
add sync and async variants where possible
refer to existing code files and the folder structure when adding something
This project uses CSharpier for code formatting. You can format your code with dotnet csharpier ..
Add new extension methods
To add new methods follow these steps:
Add methods for Result and Result<T> to CSharpFunctionalExtensions.HttpResults.ResultExtensions
Add methods for Result<T,E> to CSharpFunctionalExtensions.HttpResults.Generators.ResultExtensions and add the class to ResultExtensionsClassBuilder
Add methods for UnitResult<E> to CSharpFunctionalExtensions.HttpResults.Generators.UnitResultExtensions and add the class to UnitResultExtensionsClassBuilder
Add tests for all new methods to CSharpFunctionalExtensions.HttpResults.Tests
